It is well known that thrombin having a blood coagulant action acts upon fibrin to produce a fibrin monomer, the fibrin monomer polymerizes to form a network of fibrin fiber and, at the same time, the network takes blood corpuscles into itself to yield a thrombus with which bleedings are stopped.
Although thrombin usually exists in living body as inactive prothrombin, it can sometimes be activated little by little to give thrombin. However, the thrombin is neutralized by antithrombins which simultaneously exist in the living body, so that coagulation of blood does not take place immediately.
In cases of disseminated intravascular coagulation (DIC) and fibrinopenia, the activation of prothrombin in living body is abnormally accelerated and surpasses the neutralizing action of antithrombins, followed by the occurence of coagulation of blood and forms thrombin in various localities of living body.
Accordingly, abnormalities such as DIC can be remedied by reinforcing the antithrombin action. Substances having in vivo antithrombin activity include antithrombin-III, fibrin and its decomposition products, .alpha..sub.2 -macroglobulin and the like, among which antithrombin-III has the strongest activity so that production of a stable preparation therefrom is awaited.
Antithrombin-III herein referred to is a substance having an ability to inactivate human thrombin. It can be recovered from whole blood, plasma or serum of human. A serum expressed out of coagulated blood contains this substance, which cannot coagulate purified fibrinogen.
As the methods for purifying antithrombin-III, aluminum hydroxide adsorption method, DEAE-cellulose ion-exchange chromatography method and heparin-Sephalose adsorption method (Japanese Patent Kokai (Laid-Open) No. 35017/1973, U.S. Pat. No. 3,842,061) can be referred to. Though antithrombin-III obtained by these methods is relatively stable in a liquid state, the loss of antithrombin-III is rather significant at the time of freezing or freeze-drying which are generally considered most effective for the long term stabilization of proteins and the like.
Since antithrombin-III has some stability in liquid state, it may be possible to produce a liquid preparation of antithrombin-III. However, liquid preparation is undesirable because of the fault that activity of liquid preparation decreases after a long period of storage and deposition of insoluble matter can occur in some lots.
Although several processes for purifying antithrombin-III have already been reported as above, the process for producing a medical preparation therefrom is not yet accomplished, which is due to the fact that no technique has been developed for stabilizing the purified product for a long period of time.
The present inventors conducted a continuous study on the process for making antithrombin-III into a preparation and the method for stabilizing antithrombin-III during freeze-drying. As the result, the inventors succeeded in discovering a stabilizer useful for the purpose and developing an antithrombin preparation containing a freeze-dried antithrombin-III as a main ingredient in a form secure and stabilized for a long period of time. Based on this success, this invention was accomplished.